Problem: $ { \left[\begin{array}{rrr}{1} & {2} & {3} \\ {-2} & {-2} & {1}\end{array}\right]+\left[\begin{array}{rrr}{-1} & {-1} & {3} \\ {-2} & {3} & {3}\end{array}\right] = {?} } $
Answer: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rrr}{1}+{-1} & {2}+{-1} & {3}+{3} \\ {-2}+{-2} & {-2}+{3} & {1}+{3}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rrr}{0} & {1} & {6} \\ {-4} & {1} & {4}\end{array}\right]}$